Flywheel technology dates back to the days of early steam power systems when flywheels were used to provide continuity of motion for the long and uneven power strokes. Such applications were feasible since the rotational speed of the steam engine shafts were usually less than 500 RPM. With increased engine speeds, the use of flywheels as separate and distinct components greatly diminished. However, with the recent need for increased fuel efficiency in automobiles, flywheels have become important sources of stored energy. Specifically, conventional non-flywheel vehicle powertrain systems are inefficient since powertrains are sized only for peak power requirements. Energy is expended and thus lost during idle, low power driving or braking. To alleviate these losses current vehicle flywheel systems use a flywheel as a supplement to existing powertrains to effectively conserve energy loss. However, current systems contain drawbacks that reduce their effectiveness.
For example, a recent flywheel prototype was described in the article, "The Design of An Engine Flywheel Hybrid Drive System for a Passenger Car" by Schilke et al. which discloses an engine flywheel hybrid drive for a compact car that utilizes a flywheel to reduce peak power demands on a conventional car engine. The flywheel is used to recover braking, to reduce peak power demands and to provide a second energy source during idle or unpowered decelerations. The Schilke et al. flywheel is not arranged as an in-line drive component in the powertrain but as a supplementary power source outside the powertrain. Thus, the energy saving capacity of the flywheel is not maximized and the transmission and control scheme to effectuate flywheel power is necessarily complex.
Other systems have employed flywheels as generators for powering electric motors. For example, the General Electric Company has developed a full-size commuter bus using a flywheel-based electric propulsion system. The system is based on a three thousand pound flywheel that powers the bus after being appropriately charged and then recharged along the bus route. The flywheel is used as the main source rather than relying on another engine or motor. The main disadvantage of this arrangement is that the flywheel is used to store kinetic energy which is then converted to electricity and finally back into kinetic energy of the vehicle motion. Furthermore, an extremely large and heavy flywheel is necessary which is unworkable for an ordinary passenger vehicle. Finally, the configuration is impractical for long range purposes. The General Electric flywheel must be recharged every 3.5 miles so that it is only practical for short commuter distances having electrical cables.
A further problem with current flywheel designs is the limitations that their construction places on flywheel containment housings. Because of the necessity of designing a flywheel of appropriate size and dimension to maximize inertia, flywheels have to be relatively large and turn at relatively high RPM's to store sufficient energy to drive/power a vehicle. The containment of the flywheel thus represents a significant technical challenge: it must be sufficiently confined so that catastrophic events, such as an accident or a bearing failure, do not cause the flywheel to break free and injure bystanders. Finally, the design must be compact, lightweight and cost efficient. Current systems, however, fail to provide a flywheel with high energy storage capacity whose overall system weight is minimized and whose operations are safe for small vehicles.